1. Field of the Invention
The present invention relates generally to an elutriation method and apparatus for de-shotting mineral fiber. More particularly, this invention relates to a battery of elutriation vessels, which are arranged in series one after another, through which an aqueous dispersion of mineral fibers is passed in order to remove from the mineral fibers the shot which is contained therein.
2. Description of the Prior Art
The resistance of asbestos fibers to thermal and chemical attack makes these fibers ideally suited for a wide variety of applications. However, the employment of asbestos fibers in recent years has been significantly curtailed because of health hazards associated with their use in many situations. Accordingly, there is a need to substitute for the asbestos fibers other materials having similar properties. Mineral fibers offer a prime replacement material because of their excellent properties, but they often contain considerable amounts of shot or unfiberized particles, which are highly undesirable in certain uses of the mineral fibers.
Various processes and equipment have been developed for removing the undesirable shot from mineral fiber. Included among the methods of producing "clean," i.e. "shot-free," mineral fiber are fiber washing procedures, such as those disclosed in U.S. Pat. No. 3,055,498 and British Patent Specification No. 1,537,117. Although prior art shot removal processes have met with a measure of success, these systems often suffer from serious drawbacks. Many times they are unduly complex in design and/or equipment. They often are incapable of accomplishing a selective removal of the shot, as, e.g., of the larger size and frequently most troublesome particles. A process with the capability of selectively removing the larger size shot particles is economically attractive since, by leaving smaller unobjectionable shot particles in the mineral fiber, it adds to the total amount of salable product. Furthermore, not only have previous processes commonly failed to satisfactorily remove the entangled shot, but they have also in some cases even brought about a difficultly handleable lumping or sticking together of fibers. Additionally, many known de-shotting procedures unfortunately cause fiber breakage as well as shot removal.
It would be highly desirable if an improved apparatus and method for de-shotting mineral fiber could be found which avoid these and other disadvantages of the prior art, and result in the production of a fiber material which is useful in replacing asbestos, as a filler in fiber glass roofing mat and related products, and the like.